1. Field of the Invention
The present invention is directed to a method for fastening a rebound stop to a piston rod of a vibration damper and to the piston rod/rebound stop assembly produced in so doing. Vibration dampers having a piston rod/rebound stop assembly as component part are well known in the automobile industry. These vibration dampers comprise at least one working cylinder which is at least partially filled with a damping medium and at least one piston arranged inside the working cylinder so as to be axially displaceable with respect to the longitudinal axis of the working cylinder and which divides the working cylinder into two working chambers. The piston is connected on one side to a piston rod which is sealingly guided out of the working cylinder through a piston rod guide and is fixed to a further fastening component part of a motor vehicle. The piston generally has at least one orifice which joins the two working chambers and at least one throttle disk which at least partially covers the orifice on one side.
Conventionally, the end of the working cylinder remote of the piston rod is closed by a cylinder base and is at least indirectly arranged at a component of the motor vehicle that supports the vehicle wheel. When the piston is axially displaced inside the working cylinder, one working chamber becomes smaller and the other working chamber becomes larger. The relative change in size of the two chambers results in a pressure difference between the two chambers which allows the damping medium to flow out of the smaller working chamber through the orifice of the piston into the larger working chamber. The throttle disk inhibits the flow of the damping medium, which causes a damping effect.
2. Description of the Prior Art
In some operating conditions, for example, when driving over potholes, that the piston will move at a greater velocity in direction of the piston rod guide and strike the latter. This can lead to a leak in the piston rod seal or can damage the piston. To avoid this, vibration dampers are outfitted with a rebound stop that is axially fastened to the piston rod and serves to prevent the above-described collision between piston and piston rod guide.
The rebound stop can be fastened to the piston rod in different ways. It can be welded to the piston rod or connected to the piston rod in some other way by bonding. Since the piston rod is a highly precise component part that ideally may not have any deformations after the piston rod is fabricated, the bonding connection between the rebound stop and the piston rod is very inconvenient and entails high costs.
Further, the piston rod can have a circumferential groove as disclosed, for example, in DE 78 10 988 U1. The groove receives a snap ring and secures a rebound stop axially to the piston rod. This fastening method is common. To fasten the snap ring to the piston rod, the snap ring must be opened so that it can pass over the portion of the piston rod preceding the circumferential groove, if possible without contacting this portion. The snap ring then engages in the circumferential groove of the piston rod and secures the rebound stop axially to the piston rod. In addition, a possibility for axial fastening must be implemented for fixing the snap ring to the piston rod so that the snap ring cannot slip out of the groove under heavy loading of the rebound stop. Therefore, the above-mentioned fastening can also be cost-intensive.
A positive-engagement connection of the rebound stop to the piston rod can also be implemented in that the rebound stop is axially fastened to the piston rod through pressing as is disclosed in DE 78 10 988 U1 or DE 85 20 989 U1.
DE 10 2011 089 140 B3 also shows a rebound stop which encompasses around the piston rod in circumferential direction and which is axially fastened to the piston rod between the piston and the piston rod guide. The rebound stop is connected to the piston rod by frictional engagement. According to the constructional variant shown in DE 10 2011 089 140 B3, the piston rod has a circumferential groove, and the rebound stop is pressed into the groove to implement the positive-engagement connection between the piston rod and the rebound stop.
A fastening method having at least two method steps, for example, is known from the prior art. In the first method step, a rebound stop is positioned at a piston rod. The rebound stop encompasses the piston rod in circumferential direction and has a disk-shaped portion and, adjacent thereto, a tubular portion facing the piston rod. The piston rod has a circumferential groove.
The rebound stop is axially supported by the disk-shaped portion at a first tool component and is axially positioned such that the tubular portion of the rebound stop at least partially covers the circumferential groove of the piston rod. In the second method step, a second tool component encompassing the piston rod in circumferential direction is brought into contact with the tubular portion of the rebound stop. The contact surface of the second tool component is sloped, in particular the surface is conical, with a constant pitch, and the cone narrows radially inwardly in direction of the piston rod.
The first tool component and the second tool component then carry out an axial relative movement with respect to the longitudinal axis of the piston rod directed toward one another so that the distance between the two tool components is reduced to a defined final dimension.
In this respect, the second tool component exerts a pressing force directed axially in direction of the disk-shaped portion and a pressing force directed radially inward, i.e., toward the center of the piston rod, on the tubular portion of the rebound stop and presses the latter into the circumferential groove of the piston rod.
A disadvantage of this solution is that as the distance between the tool components decreases an increasingly greater radial pressing force is required to allow an optimal pressing and, therefore, an optimal contact of the tubular portion of the rebound stop in the circumferential groove of the piston rod.
A decrease in the axial pressing force during the decrease in the distance between the tool components is not desirable because this would inevitably lead to rapid tool wear.